The voltage produced by the CdS sensors stretches
from between zero and five volts, and is connected to
two of the PropBOE’s analog inputs — pins marked AD0
and AD1 (these are located near the bottom left of the
board). The value of 22 kΩ for the resistors connected
to each CdS cell is determined by trial and error. You
may want to try different values to find the best
sensitivity for the photocells you’re using. You want the
highest sensitivity while maintaining the widest possible
swing between zero and five volts.

As you read in Part 2 of the Beginner Bot series, the
Seeedstudio L298 H-bridge module requires at least two
inputs per motor. The direction of the motor is
determined by the instantaneous value of these two
inputs, according to Table 1.

You control the operation and direction of either
motor by setting the pins LOW (zero volts) or HIGH ( 3. 3
volts). You’ll see exactly how this is done next.

As you develop your robots, you always want to
test each new feature or component you add to them.
Refer to Listing 1 for a demonstration program for
checking the basic operation of the PropBOE, the H-bridge, and the motors.

Download this program and its additional library
from the SERVO website into the Propeller Tool
development environment, then:

1. Place a small block under the Beginner Bot base
to lift the wheels off your worktable.

2. Connect the battery to apply power to the H-bridge, and the nine volt battery to the PropBOE.

3. Plug in the programming cable between your PC
and the PropBOE. Start the Propeller Tool IDE
program (included in the Propeller software
download), and choose the Run->Identify
Hardware command (or press F7). The software